The present invention relates generally to range and speed measuring equpiment and, more particularly, to laser range and speed measuring equipment of the type utilizing a noise modulated laser signal and means for mixing signals returned from a target with a reference signal.
An aircraft radar altimeter with a transmitter frequency modulator controlled by a noise-frequency generator is described in Lange, "Signale und Systeme, Band 3-Regellose Vorgange," VEB Verlag Technik, Berlin 19, pp. 339-342, and in Horton, "Noise Modulated Distance Measuring Systems," IRE Vol. 47, p. 821 (May 1959). The signal produced by the noise-frequency generator is supplied via an RC form filter and a receiver mixer stage to which a limiter with subsequent linear discriminator is connected via an audio frequency amplifier. Part of the energy radiated by the antenna is immediately and without delay fed into the mixer stage by the receiver antenna to be used as the oscillator voltage for the mixer stage (homodyne receiver). Measuring equipment of this type is characterized in that its sensitivity for distance variations is greatest at short distances, and is largely unaffected by the characteristics of the measuring path, especially with respect to signal attenuation.